Step 1: Understanding the Question:
The question asks for the fundamental mechanism of chemical bonding that defines a covalent bond.
Step 2: Detailed Explanation:
Covalent Bonding: This occurs primarily between non-metal atoms with similar electronegativities. Atoms "share" valence electrons to achieve a stable, full outer shell (octet rule).
The electrostatic attraction of the shared electron pair to the nuclei of both atoms holds them together.
Distinction from other bonds:
Ionic Bond (Transfer of electrons): Formed when one atom gives up electrons to another, resulting in positive and negative ions held by electrostatic attraction (e.g., NaCl).
Metallic Bond (Presence of free electrons): Found in metals where valence electrons are delocalized and form a "sea of electrons" around stationary positive metal ions.
Intermolecular forces (Attraction between ions/dipoles): Generally weaker forces like van der Waals or hydrogen bonding.
Step 3: Final Answer:
Sharing of electrons is the basis for covalent bond formation.